This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9704859-9 filed in Sweden on Dec. 23, 1997; the entire content of which is hereby incorporated by reference.
This invention relates to a method and a device for regulating the transmitted phase of a signal in an antenna device.
Within systems based on electromagnetic signal transmission, for example radar systems and systems for wireless communication, phase-controlled antennas are a technique which has many advantages. These advantages include the fact that phase-controlled antennas greatly increase the ability to adaptively vary the directivity of an antenna, which for example makes it possible to have the antenna""s radiation diagram, the antenna beam, follow a moving object without mechanical movement of the antenna.
As the directivity of a phase-controlled antenna can be varied adaptively, it is possible in a system for wireless communication, for example a mobile telephone system, to direct the antenna beam towards only those directions where there are subscribers at the moment. In this way, the total transmitted power can be reduced while at the same time maintaining communication with all the subscribers in the system.
Because of the ability to vary the directivity of phase-controlled antennas, it is also possible, using a mass-produced phase-controlled antenna, to individually design the antenna""s coverage depending upon the topography of the area in which the antenna is located. For example, antennas which are located along motorways can be given a main coverage which coincides with the lengthways extent of the road and antennas which are placed at intersections can be given a main coverage which coincides with the extent of the intersection.
A phase-controlled antenna is normally formed of a large number of antenna elements whose antenna beams together form the resultant antenna beam of the phase-controlled antenna. The resultant antenna beam is controlled by varying the phase of the signals that are sent out by the antenna elements making up the antenna. In other words, in a phase-controlled antenna it is of the utmost importance that the phase of the signal transmitted by each antenna element is the intended one.
The antenna elements in a phase-controlled antenna often include a phase shifter which causes the signal to assume the required phase, and a power amplifier, PA, connected to the phase shifter, which amplifies the signal. A problem in this context is that the power amplifier can affect the phase of the signal transmitted by the antenna element. These phase shifts in the power amplifier arise, for example, as a result of the temperature in the power amplifier varying, which can occur when the output energy varies.
In other types of antenna than phase-controlled group antennas there can also be power amplifiers which can affect the phase of the signal in an unwanted way. An example of such an antenna is a group antenna which is not phase-controlled, in other words an antenna whose beam is not controlled electronically but where the antenna as a whole still consists of a number of antenna elements. Each antenna element in such a group antenna can include a power amplifier. The phase of the signal which is fed into each antenna element in this type of group antenna may not be affected by the power amplifier.
Phase shifts which arise due to power amplifiers in systems of the type described above can be compensated for by the power amplifier being reconnected to the phase shifter in a control loop. In such a control loop there are means for controlling the phase shifter whereby the phase shifter is made to cause the power amplifier to assume the required phase. A problem in this context is that many types of phase shifter do not have so-called periodic behaviour, in other words the phase shifter only has a certain linear range within which it is required to work. Phase shifters without periodic behaviour should be reset to a working point, a so-called modulation position, within the linear range before the phase shifter has gone outside its linear range.
There is therefore a need at certain times to reset a phase shifter which is part of an antenna element of the types described above to a certain predetermined modulation position. Resetting of phase shifters should not be carried out when the signal transmitted by the antenna element contains information, as the resetting could then affect the transmission of information. An additional requirement is that the modulation position to which the resetting of the phase shifter is carried out should be such that the phase shifter cannot go outside its linear range before the next resetting occasion.
Document WO94/10765 describes a device for linearization of a power amplifier in a mobile telephone system of the TDMA type. The linearization of power amplifiers according to this document can only be carried out at certain predetermined times, so-called linearization time slots. This could be said to result in a rather inflexible system.
Documents U.S. Pat. No. 5,426,641 and JP 9 116 474 describe devices for regulating the phase of the transmitted signal in systems for wireless communication. The devices according to these documents include measuring the phase position or parameters relating to the phase position of the component which exhibits variations in phase, after which measurements calculations are carried out to find out what modulation position the component in question should be reset to. These appear to be rather complex and thus expensive solutions.
The problem which is solved by the invention is thus to be able to regulate correctly the phase of the signal in a device which is part of a system for electromagnetic signal transmission, preferably an antenna element in an antenna which is part of a system for wireless communication, without the phase regulation having an adverse effect on the transmission of information within the system.
The device which is regulated according to the method preferably comprises a phase shifter which has a linear and a non-linear range, a power amplifier which amplifies the signal from the phase shifter and means for controlling the modulation position of the phase shifter, by which the transmitted signal is given the required phase position.
The above-mentioned problem is solved according to the invention by utilizing advance knowledge of when the transmitted signals contain information and when they do not. At times when the signal does not contain information, the phase shifter is reset to a certain predetermined modulation position, which preferably lies within the linear range of the phase shifter.
In a preferred embodiment the invention is used in a TDMA mobile telephone system of the GSM type.